Changing the shape and color of hair represents an important area of modern cosmetics. For stylish coloring of hairstyles or for concealing gray or even white hair with fashionable or natural hues, the consumer turns to color-changing agents.
For changing the color of keratinic fibers, in particular human hair, those skilled in the art are familiar with various systems, depending on the requirements for the coloring or the change in color.
So-called oxidation dyes are used for long-lasting, intensive colorings having appropriate fastness properties. Such coloring agents customarily include oxidation dye precursors, so-called developer components and coupler components. The developer components form the actual dyes with one another under the influence of oxidizing agents or atmospheric oxygen, or by coupling with one or more coupler components. The oxidation dyes are generally characterized by intensive, excellent, long-lasting color results. For naturally acting colorings, a mixture of a fairly large number of oxidation dye precursors may be used; in many cases, direct dyes are additionally used for shading.
Despite their advantageous coloring properties, oxidative hair dyes have drawbacks. In particular for some of the common oxidation dye precursors, including p-phenylenediamine, it is suspected that for many consumers they may have an irritating effect and thus cause sensitization or even allergic reactions. Therefore, for these substances there is a need for further improvement with regard to their physiological compatibility profile. Many compounds have been investigated in the search for replacement substances, but these often have application-related problems, in particular insufficient leveling properties. In addition, despite the existence of highly developed coloring systems, there is still a need for coloring systems which achieve excellent luminosity and intensity of coloration, and which do not lose these properties even under the effect of external environmental influences such as irradiation by sunlight or washing the hair.
It is therefore desirable to reduce the above-mentioned disadvantages of oxidative hair coloring agents. The coloring agents should produce intensive colorings with high color intensity and good resistance to external influences, in particular with good light fastness and wash fastness, and which do not experience lightening or shifting of the color, even after intensive irradiation with sunlight and multiple shampooings of the hair. Furthermore, the colorings should preferably have excellent leveling properties and should be less selective, i.e., achieve preferably uniform, consistent color results on hair which has been pretreated in various ways. In addition, the coloring agents should have a toxicologically advantageous profile.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with this background of the invention.